Gas ignition system employing piezoelectric element



June 9, 1964 E. J. WEBER 3,135,355

GAS IGNITION SYSTEM EMPLOYING PIEZOELECTRIC ELEMENT Filed Dec. 14, 1962 INV ENT'ORI BY EARL J. WEBER ATTYS.

United States Patent 3,136,355 GAS IGNITION SYSTEM EMPLOYING PIEZO- ELECTRIC ELEMENT Earl J. Weber, Bay Village, Ohio, assignor to American Gas Association, Incorporated, New York, N.Y., a corporation of New York Filed Dec. 14, 1962, Ser. No. 244,706 5 Claims. (Cl. 158-123) This invention relates to gas burner systems, and particularly to such systems which utilize automatic electrical ignition of a gas.

Systems for the ignition of gas burners by electrical means are generally characterized by the advantage that they require no perpetual pilot flame with its attendant waste of fuel and unnecessary heating of the room. It is often desirable that such ignition systems be operable independently of the availability of external electrical line power and yet not require a local battery, and it is generally undesirable to require the operator of the burner to apply personally to the system the energy needed for the ignition process.

The present invention provides automatic electrical ignition of a gas burner without requiring external application of electrical power or a local battery, and without requiring any appreciable application of energy by the operator to produce the ignition. This is accomplished by using changes in the compressive forces on a piezoelectric cell to generate the ignition voltage for a given burning period of the burner, and by generating the compressive forces on the piezoelectric cell in response to heat energy produced during an earlier burning period. More particularly, in a preferred form of the invention a part of the energy from the heat of the burner produced during an earlier burning period is converted to stored mechanical energy and released at a later time in response to turningon of the burner control, but without appreciable effort by the operator, to generate the required ignition voltage.

For example, a thermally-expandable rod may be heated during a given burning period and the resultant expansion of therod used to force a compressing member against the piezoelectric crystal. A mechanical latching arrangement then engages the compressing member and holds it in its compressive position even'after termination of the burning period'and consequent contraction of the rod. When at a later time the gas control is turned on, an easily-operated trip mechanism linked to the gas control releases the latch and thus suddenly removes the compressive forceson the crystal. This sudden unstressing of the crystal generates a piezoelectricv high-voltage across the crystal which is applied to discharge electrodes situated adjacent the burnerto produce sparks for igniting the emanating gas.

Other objects and features of the invention will be more readily appreciated from a consideration of the following detailed description taken in connection with the accompanying figure, which is not necessarily to scale, and which illustrates a preferred embodiment of the invention partly diagrammatically, partly in section, and partly in full.

Referring now to the embodiment shown specifically in the figure, a conventional gas burner is supplied with suitable fuel gas through an inlet pipe 12 by way of an ordinary rotary gas valve 14, which is manually operable in the usual way to turn the gas supply on and off and to vary its rate of flow depending on the angular position of the control for the valve. A conventional pilot gas supply element 16 is arranged adjacent burner 10 and supplied with gas by way of valve 14 through appropriate piping (not shown). In operation, the valve 14 is turned on to supply gas to the burner 10 and to the pilot gas supply element 16, and the gas emanating from pilot 16 is ignited by a spark discharge between electrodes 18 to produce an ignition flame 20 disposed so as to ignite the gas emanating from the burner 10,

Mounted adjacent burner 10 and in a position to be heated by burning gas from the burner is a thermally-expandable rod 24 having one end rigidly affixed to the closed end 26 of a rigid casing 28, the casing 28 having a lower coeflicient of thermal expansion than rod 24 and being rigidly mounted to the fixed supporting chamber 30 at wall 31 thereof. The rod 24 extends through the wall 31 so as to be slidably supported thereby. Accordingly the free end 32 of rod 24 moves to the leftin the figure as it expands due to heating by burner 10. It will be understood that the rod 24 and casing 28 are positioned with respect to the burner so as not to interfere with its normal heating function, as by placement near the periphery of the burner or beneath the support on which objects to be heated are placed.

Expansion of rod 24 is used to compress the piezoelectric crystal 34 which is conductively mounted on a wall 35 of the fixed chamber 30. Crystal 34 is conventionally constituted and arranged so that upon rapid stressing or unstressing thereof by mechanical means a high voltage is generated between its opposite faces suitable for application to a spark-discharge system, such as electrodes 18, to produce an electrical discharge therebetween. Such elements are now well known in the art and hence their nature and operation need not be described here in detail.

As an example only, the piezoelectric element may be of barium titanate or lead titanate zirconate.

To apply the,voltage generated across the crystal 34 to the discharge electrodes 18, the wall 35 to which one face of the crystal is mounted may be made of electrically-conductive material, and a suitable conductive lead member 36 connected between this wall and one of elec trodes 18, while a metallic layer 38 may be provided on the opposite face of the crystal and a suitable conductive lead 40 connected between layer 38 and the other of the spark-discharge electrodes 18. :Lead 40 extends through an opening in the chamber 30 so as to be electrically insulated therefrom, and an electrically-insulating layer 42 disposed over conductive layer 38 insulates the crystal from a pointed pressure-transmitting element 44;

Upon thermal expansion of rod 24 pressure is applied to the point or protuberance of element 44 by means of a lever 48 pivoted about a fulcrum 50. Thus when rod 24 is cool it bears against the lower end of lever 48, which is then in the position 48A shown in dotted outline, in which position no appreciable pressure is applied to the piezoelectric crystal 34. However, as rod 24 expands it presses against the lower end of lever 48, causing it to move to the left to the position shown in full-line in which position the lever exerts upon the crystal 34 a compressive force sufliciently great that, when this force is later removed suddenly, a voltage is generated across the crystal which is sufiicient to produce a spark-discharge between electrodes 18. v

Arranged above the upper end of lever 48 is a latching arrangement adapted to latch lever 48 in place once it has reached the position in which it applies the required compressive force to the crystal 34. In the present embodiment this latching arrangement comprises a spring-biased lever arm 52 mounted to pivot about a fulcrum 54- on a support 56 rigidly mounted to fixed chamber 30. The spring-bias is provided by a compressed spring 58 mounted between the support 56 and the upper side of lever arm 52 so as to urge the left side of that lever downward. A detent or notch 60 is provided near the left-hand end of lever 52, and the extreme left-hand end of lever 52 and the rest position of the lever in the absence of applied forces are so arranged that when the upper end of lever 48 moves from the position shown in dotted outline to that shown in full, it slides along the underside of the left-hand end of lever 52 and then falls intothe detent 60. In this position the lever 48 is held by the arm 52 so as to exert the desired compressive force on crystal 34 even after cooling of rod 24 has removed the force acting at the lower end of lever 48.

Means are also provided for releasing the latching arrangement and thereby removing the compressive forces from crystal 34 when the gas control 14 is turned on to supply gas to the burner. In the present embodiment this means comprises a rotary cam 60 mechanically linked to gas valve 14 so that when the valve is turned to the position for which sufiicient gas for ignition issues from pilot 16 and burner 10, the cam surface of cam 60 moves the right-hand end of lever 52 downwardly and the left-hand portion upwardly to release arm 48 from detent 60.

In operation, burning gas from burner it) heats rod 24, causing it to expand slowly and to press against the lower end of arm 48 thereby exerting a compressive force upon piezoelectric 34 and, at the point of rotation of lever 48 for which suflicient compression has been applied, the lever 43 is latched into position to maintain this compressive force even when rod 24 cools. Accordingly, when gas valve 14 is turned off the compressive force remains on crystal 34. When valve 14 is turned on at a later time it actuates cam 60 to release the latching arrangement, thus unstressing crystal 34 to produce a large output voltage across the discharge electrodes 18 and to light the pilot flame 20 and the burner 10. The point of rotation of valve 14 at which cam 60 is actuated to release the compression of crystal 34 is such as to allow gas sufficient for ignition to reach the pilot 16 and the burner before the spark is generated at electrodes 18.

It will be appreciated that in this arrangement the compressive forces acting on crystal 34 are generated in response to heat energy from the burner 10 produced during one burning period thereof, this energy of compression being effectively stored in mechanical form by the latching mechanism until a later time at which the burner is again turned on, at which time the stored energy is released by unlatching to provide the ignition sparks. While the unla-tching is provided in response to operation of the control by the operator, the energy required for this can be extremely small, the energy producing ignition being derived primarily from the heat of the burner and not from the operator.

Accordingly a gas burner ignition system is provided which requires no external electrical power supply or local battery and substantially no energy input by the operator, the energy for ignition instead being generated by the heat of the burner and stored from the time the burner is turned off until a later time at which it is needed for a subsequent ignition.

It will be understood that other modes of application of voltage-generating forces to the crystal 34 and other arrangements for storing energy between burning periods may be employed, as will occur to one skilled in the art.

For example, the energy of expansion of rod 24 may be stored in the compression of a spring which is latched in a stressed condition until subsequent operation of the lburner control releases the spring to apply to the crystal 34 compressive forces which generate the igniting discharge.

Ignition of the burner for the first time can be provided conventionally as by lighting with a match, or by a manual arrangement for pressing lever 48 into its compressing position.

While the invention has been described with particular reference to specific embodiments thereof it will be understood that it may be embodied in a variety of forms differing from those specifically described, without departing from the scope of the invention as defined by appended claims.

I claim:

1. A gas burner and ignition system, comprising:

a gas burner to be ignited;

a gas control for said burner;

a piezoelectric element responsive to changes in compressive forces thereon to generate voltages for igniting said burner;

igniter means responsive to voltages generated by said piezoelectric element to ignite gas from said burner;

means responsive to heat generated by said burner during a given period of its burning to produce stored mechanical energy; and

means responsive to a later operation of said gas control for releasing said stored energy to change said compressive forces on said piezoelectric element.

2. A gas burner and ignition system, comprising:

a gas burner to be ignited;

gas control means for controlling the flow of gas to said burner;

igniter means responsive to voltage applied thereto to produce a spark discharge for igniting said burners;

a piezoelectric element connected to said igniter means and responsive to removal of compressive forces applied thereto to generate voltages for operating said igniter;

thermally-responsive means disposed so as to be heated by said burner during a given period of its burning and responsive to heating to change size;

means responsive to changes in size of said thermallyresponsive means to apply compressive forces to said piezoelectric element;

releasable means for maintaining said compressive forces after said given burning period is ended; and

means responsive to operation of said gas control means after said given burner period is ended torelease said releasable means, thereby to remove said compressive forces and to produce voltages for operating said igniter.

3. A gas burner and ignition system comprising:

gas burner means;

igniter means responsive to a voltage applied thereto to produce a spark discharge for igniting gas emanating from said gas burner means;

a piezoelectric crystal responsive to changes in compressive forces applied between different faces thereof to produce a voltage between said faces;

means electrically connecting said opposite faces of said crystal to said igniter means;

a thermally-expandable member disposed adjacent said gas burner means to receive heat from said gas burner means during a predetermined burning period thereof and to expand in response thereto;

means responsive to expansion of said member to pro duce stored mechanical energy;

a gas control adjustable to turn on and off the supply of gas to said gas burner means; and

means responsive to turning-on of said gas control after said predetermined burner period for releasing said stored energy and for applying it to change the compressive forces across said crystal, whereby a voltage is generated across said crystal and applied to said igniter means to produce a spark discharge for igniting said burner means.

4. The method of igniting a gas burner which comprises:

operating said burner during a given burning period thereof to produce a burner flame;

heating a heat-responsive energy-storage device with said flame during said burning period to store energy of said flame in said energy-storage device;

applying said stored energy in mechanical form to a piezoelectric element so that release of said stored energy alters the stresses in said piezoelectric element sufficiently to generate an electrical spark for ignition of said burner; and I 5 stored in mechanical form from the end of said given burning period to the time of said subsequent turning-on of said burner.

References Cited in the file of this patent UNITED STATES PATENTS Ray Apr. 18, 1944 Harlmess Sept. 13, 1955 

1. A GAS BURNER AND IGNITION SYSTEM, COMPRISING: A GAS BURNER TO BE IGNITED; A GAS CONTROL FOR SAID BURNER; A PIEZOELECTRIC ELEMENT RESPONSIVE TO CHANGES IN COMPRESSIVE FORCES THEREON TO GENERATE VOLTAGES FOR IGNITING SAID BURNER; IGNITER MEANS RESPONSIVE TO VOLTAGES GENERATED BY SAID PIEZOELECTRIC ELEMENT TO IGNITE GAS FROM SAID BURNER; MEANS RESPONSIVE TO HEAT GENERATED BY SAID BURNER DURING A GIVEN PERIOD OF ITS BURNING TO PRODUCE STORED MECHANICAL ENERGY; AND MEANS RESPONSIVE TO A LATER OPERATION OF SAID GAS CONTROL FOR RELEASING SAID STORED ENERGY TO CHANGE SAID COMPRESSIVE FORCES ON SAID PIEZOELECTRIC ELEMENT. 